Chemical plants, oil refineries and other industrial facilities produce fluids which present health and safety problems. In some situations, even small amounts of the fluid, for example, a few parts per million or even a few parts per billion, can constitute serious health, safety and environmental problems. Also, such fluids and gases can be a danger to workmen in the vicinity of the facility. The difficulties in detecting and determining the presence of a selected fluid in a process stream or in the environment is exceedingly difficult due to the extensive nature and the large size of industrial plants.
Thus, the detection and monitoring of fluids associated with industrial plants is highly advantageous with respect to health, safety and environmental concerns. Further, the detection and monitoring of industrial fluids can prevent other dangers such as ignition, plant failure and the like.
Further, the need to detect particular constituents in a process stream can be based on product quality, process control, regulatory requirements and financial considerations. Particular fluid constituents of interest are, for example, hydrogen sulfide and nitrogen oxides. Industrial monitoring equipment exists for all phases of industry. Particularly, a variety of equipment is available using colorimetric methods. Colorimetric monitoring is utilized in process streams and associated atmospheres in and about industrial facilities. The colorimetric equipment and methods that are prevalent include absolute darkness techniques, tape difference techniques and analog first derivative techniques. Typically using colorimetric equipment, an ambient atmosphere is passed through the apparatus whereby the fluids in question react with a color-altering material. The magnitude of the color change is proportional to the concentration of the fluid in the atmosphere.
All colorimetric methods have problems. For example, absolute darkness techniques are subject to noise from zero fluctuation. The noise from zero fluctuations is due to the non-uniform reflectance characteristics of the colorimetric sensing media. Similarly, tape difference techniques require a zero reading. After the zero reading, a period of time must elapse between the initial reading and the final reading. The relatively long time period between readings does not take into account the nonlinearity of the sensing media and effects the response time of tape difference techniques. Analog first derivative techniques are subject to power line interferences. Further, analog first derivative techniques are limited by the current leakage in the differentiating capacitor which is typically used. Still further, the analog first derivative techniques operate in the linear portion of the response of the sensing device and require a linear response curve relationship for accurate results.
Many colorimetric analyzers generally have light sources, optics and detectors fixed in a rigid framework with light paths of the optics traversing through the ambient air. Such colorimetric analyzers require that correct alignment of the optical components be maintained during the operation of the equipment. The alignment of the optics is typically subject to environmental factors as well as mechanical problems. Examples of environmental and mechanical problems include changes in temperature, operation of equipment in high vibration environments, mechanical stress associated with typical equipment use, and the like.
Of additional concern is the environment in which the apparatus must operate. It is not unusual that the apparatus is required to be explosion proof for operation in industrial facilities. Typically, an explosion proof apparatus must be housed in a purged cabinet or housed in an explosion proof enclosure. The use of explosion proof equipment creates many problems with respect to adjustment, maintenance and calibration of the apparatus without compromising the protective environment of the explosion proof equipment.
It is, therefore, a feature of the present invention to provide an apparatus and method to monitor the concentration of a constituent in a fluid which eliminates or avoids the above discussed problems.
A feature of the present invention is to provide an apparatus and method whose measurement parameters can be changed or modified depending on the requirements of the particular analysis.
Another feature of the present invention is to provide a concentration measuring apparatus and method which utilizes a sliding derivative analysis technique.
Another feature of the present invention is to provide a concentration measurement apparatus and method that provides significant noise reduction and enhanced sensitivity.
Another feature of the present invention is to provide a concentration measuring apparatus and method which utilizes colorimetric sensing in conjunction with fiber optic means.
Another feature of the present invention is to provide a concentration measuring apparatus and method which is not effected by environmental changes, vibration and mechanical stress.
Yet another feature of the invention is to provide a concentration measuring apparatus and method which utilizes an operator interface that does not compromise explosion proof enclosures associated with such instruments.
Still another feature of the present invention is utilizing a colorimetric apparatus and method in association with a novel apparatus and method for the storage and dispensing of a reflective sensing media.
Still another feature of the present invention is utilizing a bifurcated fiber optic means that guarantees optical alignment and eliminates the need for periodic realignment.
Another feature of the present invention is to provide a concentration measuring apparatus and method which utilizes colorimetric techniques while providing that the lamp and electronics can remain in an explosion proof enclosure.
Another feature of the present invention is to provide a concentration measuring apparatus and method which utilizes colorimetric techniques including a single photocell system without the need for balancing of photocells.
Another feature of the present invention is to provide a concentration measuring apparatus and method that utilizes a specific wave length of light for increasing the contrast associated with the reflective sensing media and therefore increasing the sensitivity of the apparatus and method.
Yet another feature of the present invention is to provide a concentration measuring apparatus and method which utilizes magnetic switches for readily changing the operating parameters without compromising the explosion proof characteristics of the inventions.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.